memory

Not every computer is a performance gaming rig. Some of us need cheap laptops and tablets for simple Internet browsing or word processing, and we don’t need to shell out thousands of dollars just for that. With a cheaper price tag comes cheaper hardware, though, such as the eMMC standard which allows flash memory to be used in a more cost-advantageous way than SSDs. For a look at some the finer points of eMMC chips, we’ll turn to [Jason]’s latest project.

[Jason] had a few damaged eMMC storage chips and wanted to try to repair them. The most common failure mode for his chips is “cratering” which is a type of damage to the solder that holds them to their PCBs. With so many pins in such a small area, and with small pins themselves, often traditional soldering methods won’t work. The method that [Jason] found which works the best is using 0.15 mm thick glass strips to aid in the reflow process and get the solder to stick back to the chip again.

Doing work like this can get frustrating due to the small sizes involved and the amount of heat needed to get the solder to behave properly. For example, upgrading the memory chip in an iPhone took an expert solderer numerous tries with practice hardware to finally get enough courage to attempt this soldering on his own phone. With enough practice, the right tools, and a steady hand, though, these types of projects are definitely within reach.

[Dave] aka [Mubes] has been working on the Blue Pill platform which is a STM32F103C8 board. While they don’t natively output video, it’s a feature that provides a handy tool to have for debugging in order to see what’s going on in your code. However, if the video code takes up all of the processor power and memory there’s not much point. [Dave]’s video output program, on the other hand, takes up only 1200 bytes of RAM and 24% of the processor for a 50×18 text display over VGA, leaving a lot of room left for whatever else you need the tiny board to do.

Video output on a device this small and lightweight is an impressive feat, especially while saving room for other tasks. This brings it firmly out of the realm of novelty and into the space of useful tools to keep around. If you want to try the same thing on an ATtiny, though, you might have to come up with some more impressive tricks.

TRON is a science fiction classic, hitting cinemas in the midst of the burgeoning home computer era. It’s the film that created the famous light cycle, which spawned many video game recreations in the following years. Many years ago now, [Daniel] decided to flex his programming muscles by coding a version of the game for the Apple IIgs, with accidentally excellent results.

In the film, the characters find an escape from the light cycle game by forcing another player to crash into the walls of the play area. The resulting explosion left a hole, allowing the players to exit the light cycle game and explore the rest of the computer. Amusingly, due to a coding oversight, [Daniel] had created exactly this same flaw in his own code.

[Daniel]’s game differed from the original in that players were provided with missiles to destroy enemy trails. However, these missiles did not discriminate, and due to the simplicity of the code, were able to destroy the boundary on the play area. This was discovered when the computer player tried to escape an otherwise impossible situation. Upon blowing a hole in the arena wall, the computer player proceeded to drive off the screen – into invalid memory. This led to the computer crashing in short order, due to the unprotected memory space of the Apple II platform.

It’s a case of code imitating art – and completely by accident. The game managed to replicate the light cycle escape from the film entirely due to the unexpected behaviour of the simple missile code. [Daniel] steps through the code and how the bug happened, and covers the underlying principle behind the resulting crashes. It’s an entertaining tale of the risks of coding at low level; something we don’t always run into with today’s modern interpreted languages.

Not only is the Super Nintendo an all-around great platform, both during its prime in the 90s and now during the nostalgia craze, but its relative simplicity compared to modern systems makes it a lot more accessible from a computer science point-of-view. That means that we can get some in-depth discussion on how the Super Nintendo actually does what it does, and understand most of it, like this video from [Retro Game Mechanics Explained] which goes into an incredible amount of detail on the mechanics of the SNES’s memory system.

Two of the interesting memory systems the SNES uses are called DMA and HDMA. DMA stands for direct memory access, and is a way for the Super Nintendo to access memory independently of the CPU. The advantages to this are that it’s incredibly fast compared to more typical methods of accessing memory. This isn’t particulalry unique, but the HDMA system is. It allows the SNES to do all kinds of interesting tricks with its video output display like changing color gradients and doing all kinds of masking effects.

If you’re interested in the inner workings of classic consoles like the SNES, this video gets way down in the weeds in the system itself. It’s interesting to see how programmers were able to squeeze more capability from these limited (by modern standards) systems by manipulating memory like the DMA and HDMA systems do. [Retro Game Mechanics Explained] is a great resource for exploring in-depth aspects of lots of classic games, like how speedrunners can execute arbitrary code in old Mario games.

As usual with these research projects, there is good news and there is bad news. The good news is that — in theory — a memory device made using hydrogen lithography could store 138 terabytes per square inch. That’s enough, apparently, to store the entire iTunes catalog on a quarter. The bad news? Well, right now this takes exotic lab equipment at very low temperatures and pressures.

There are many ways of storing data in a computer’s memory, and not all of them allow the computer to write to it. For older equipment, this was often a physical limitation to the hardware itself. It’s easier and cheaper for some memory to be read-only, but if you go back really far you reach a time before even ROMs were widespread. One fascinating memory scheme is this example using a vacuum tube that stores the characters needed for a display.

[eric] over at TubeTime recently came across a Raytheon monoscope from days of yore and started figuring out how it works. The device is essentially a character display in an oscilloscope-like CRT package, but the way that it displays the characters is an interesting walk through history. The monoscope has two circuits, one which selects the character and the other determines the position on the screen. Each circuit is fed a delightfully analog sine wave, which allows the device to create essentially a scanning pattern on the screen for refreshing the display.

[eric] goes into a lot of detail on how this c.1967 device works, and it’s interesting to see how engineers were able to get working memory with their relatively limited toolset. One of the nice things about working in the analog world, though, is that it’s relatively easy to figure out how things work and start using them for all kinds of other purposes, like old analog UHF TV tuners.

We all love new tech. Some of us love getting the bleeding edge, barely-on-the-market devices and some enjoy getting tech thirty years after the fact to revel in nostalgia. The similarity is that we assume we know what we’re buying and only the latter category expects used parts. But, what if the prior category is getting used parts in a new case? The University of Alabama in Huntsville has a tool for protecting us from unscrupulous manufacturers installing old flash memory.

Flash memory usually lasts longer than the devices where it is installed, so there is a market for used chips which are still “good enough” to pass for new. Of course, this is highly unethical. You would not expect to find a used transmission in your brand new car so why should your brand new tablet contain someone’s discarded memory?

The principles of flash memory are well explained by comparing them to an ordinary transistor, of which we are happy to educate you. Wear-and-tear on flash memory starts right away and the erase time gets longer and longer. By measuring how long it takes to erase, it is possible to accurately determine the age of chip in question.